Can we develop a new detector..?

[Pulse]

Hi all,

I want to develop a new metal detecor. Is there someone here will join me for develoing ?

[Davor]

You mean something out of the Dilbert series where his boss draws a rising curve and says that he did his part, and the rest of the company must do their part (to make it happen)

If you have an idea just go ahead. Many of us will jump in to help.

I am toying with a BFO with nice audio, motion and ground compensation and some discrimination. Currently I'm working on motion compensation part. I expect 5 chips in total, out of which 2 are 555s. We'll see

[lari]

Hi all,

I want to develop a new metal detecor. Is there someone here will join me for develoing ?

[mikebg]

Pulse, my hobby is design of TXs, RXs and antennas for QRP amateur radio. According former (R)EMI group (ham radio designers), the first and most important step of a developing process is the block diagram. As an ex spokesman of (R)EMI group, I will join you for "develoing" of block diagram. Let we start with discussion on block diagram.
Unfortunately, I will have problems with collaboration in design group because in amateur radio is used frequency domain and different terminology. For example, your nickname "Pulse" means for me "wide band".
Using this terminology, my question is:
What we should develop, narrow band or wide band metal detector?

[mikebg]

I am toying with a BFO with nice audio, motion and ground compensation and some discrimination. Currently I'm working on motion compensation part. I expect 5 chips in total, out of which 2 are 555s. We'll see

Davor, a motion type BFO metal detector was developed by Macario:
Macario, R.C.V.; Discriminative Metal Detector, Wireless World, Jul. 1978, vol. 84, No. 1511. pp. 43-46
He uses the PLL IC 4046. Here is the principle:

[Davor]

Funny you should mentioned it here just after my exposing my thoughts
4046 is my choice as well, and circuitry looks kinda familiar
I am about to combine notch as a phase reference, two search oscillators working far apart, and a LO, made of VCO/PLL (e.g. 4046) to steer tone to the very notch frequency. Search oscillators are compensated so that wide range of ground proximity affected tuning results in negligible mutual frequency difference.
I expect to enjoy silence in absence of targets, nice sine with targets, and some degree of discrimination.

[Pulse]

Hi friends,

Why we couldn't use MCU for osc ? I can write the software.

[Davor]

Of course you can. You obviously consider VLF. For PI it is a very common solution.

However, a resonant tank is a premium energy conserving device, and to match that performance you'll need some sensing method to adjust MCUs output. Or abandon the resonant frequency idea altogether - which may have some not so obvious advantages. Point is that for a MCU synthesized signal you may be very certain about phase shifts necessary for Rx purposes - you obtain them directly.

[lari]

Imas Davore poruku.

[Davor]

Got it Glad to meet you here.

[rajesh]

new desine

Hi all,

I want to develop a new metal detector. Is there someone here will join me for developing ?

hi quick intently purchase a am band receiver 460 mega h. frequency is very sensitive to old buried gold you ccan try it but very poor result http://electronic-schematic.blogspot...z-am-dual.html

[Davor]

SA602 works by means of Gilbert cell, which can be employed as phase detector. It is quite old, and recent builds use bilateral switches for that purpose.

[Tepco]

hi quick intently purchase a am band receiver 460 mega h. frequency is very sensitive to old buried gold you ccan try it but very poor result http://electronic-schematic.blogspot...z-am-dual.html

Perfect, this can detect 100 tons of metal, mostly aluminum, flying above your head. Otherwise nothing to do with metal, especially gold detection, this is airband AM receiver. At a price of purchased parts, second hand scanner or ham radio equipped with airband can be found. Or even this, on junkyard:

[Tepco]

SA602 works by means of Gilbert cell, which can be employed as phase detector. It is quite old, and recent builds use bilateral switches for that purpose.

If you want perfect metal detecting disaster, try this. Sorry, hand written in hurry, but clear enough, never mind, this is pointless anyway, just operating principe is interesting. Good reminder that in electronics, things that look promising on paper can be completely rubbish when actually built. I did this ckt. long time ago, don’t even have schematic, but simple PIC based FM detector using 8pin chip and 5 other parts is better than this one. New tread named “1001 thing what not to do on MD” can start here, i’m only half way. But ckt. is interesting, see sch. below.

It consists of fast PLL, output divided by 4 using 4013 FF and used as a phase detector reference, another reference signal is created using ring counter connected 4013, now 90 deg out of phase. This signal drives coil amplifier (high Q LC resonant tank at some 40kHz ) that produce another 90 deg phase shift at resonance, so in effect PLL is locked to coil resonant frequency\phase as a reference but due to fast loop filter response will track it relatively fast.

Another slow PLL is locked to first one, now at 4x coil freq. but with much slower loop response, providing drift compensation ,and third phase detector measure phase\freq. difference between them generating target information. In effect, sort of auto tuned\stabilised two loop PLL.

This one is writeoff for me, at the end prototype become more complex than some minimalistic VLF and performed poorly as can be expected from PLL or BFO. Maybe can be used for something else however. Component limitations, like 4046 RC based VCO, not known to be low phase noise one, phase detector exhibiting large”dead zone” ,lacking response when signals are allmost zero phase due to slow logic inside the chip etc. Can be rescued to some degree using different construction, but not wort any effort. Except if someone needs detecting device at very high freqency, can be easily ten’s of MHz or more, this one is still the simplest way then.

[Davor]

Right. Fortunately we are not married to our ideas and if they perform poorly we can easily hop to another one.